Aqueous industrial cooling systems that employ cooling towers usually require chemical treating agents to prevent corrosion, scaling and other encroachments which lessen efficiency.
Historically chemical treatment has normally consisted of acid and various heavy metals which were easy to test for. These compounds also had broad application ranges over which they were effective. This made the treatment process relatively painless.
Now, circa 1988, chemical treatment of industrial cooling water is far more complex. As environmental concern has heightened, heavy metals have given way to organics, acrylamides, acrylates, organic phosphates and triazoles, etc. Unfortunately, all these new treatment programs are quite difficult to test for. Exacerbating the situation is the additional fact that virtually every one of them requires very tight control to perform in an optimum manner
Various approaches have been tried to resolve this dilemma. Efforts to simplify tests, ratio chemical feed to either system make-up or blowdown, etc., have all been examined and, by and large, found wanting
Almost all attempts to automate the precise addition of chemicals to cooling towers have been defeated by the unknown variables and unknown volumetric water changes inherent in these systems. Evaporation rates vary with changes in ambient wet bulb temperature; and cooling towers lose unknown amounts of water due to windage, drift, overflow, leaks, and uses of system water besides cooling. Also, it is common practice in many large plants to dispose of various extraneous water streams (process condensates, tramp bleeds, etc.) by returning them to the cooling tower on an unregulated basis. All these variables become unknown water gains and losses.
On the basis of these experiences, and the inability of industry to develop accurate, dependable tests for the types of treatment compounds in use, advanced technology is needed to determine the performance of the treating agent.
Research projects of considerable magnitude have been funded to find materials that can be employed as easily measurable indicies of the amount of product (treating agent) present in the system. One such project is disclosed in application Ser. No. 019,454, filed Feb. 26, 1987 now U.S. Pat. No. 4,783,314.
While the present invention addresses a system (instrumentation) for continuous monitoring, as expressed above, a background of complex chemistry is also involved because the instrumentation analyzes the concentration of a tracer (parts per million tracer=ppm T) added proportionally with the treating agent (ppm A).
The tracer must be transportable in the waste system without change In actual use, the treating agent will be consumed If actual performance of the treating agent conforms to the theoretical performance (postulated rate of consumption) the ratio of tracer to treating agent will increase.
Thus, the tracer, to serve as an index of the product or treating agent performance must fulfill several criteria.
Firstly, selected chemicals must be detectable on a continuous or semicontinuous basis. Measurements of concentration must be accurate, repeatable and capable of being performed on many different waters (i.e. clean, turbid, hard, soft, etc.).
Secondly, the tracer material cannot be one already present in a significant quantity in the water used for industrial cooling.
Thirdly, testing for the tracer cannot be interfered with, or biased, by other chemical compounds normally present in cooling water.
Fourthly, the tracer must not reduce the efficacy of such active ingredients of the treatment chemicals themselves as poly acrylic acid, poly (acrylate/acrylamide) copolymers, acrylate/acrylamide/amino methane sulfonic acid, acrylate/methacrylic acid/t-butylacrylamide, 1-hydroxyethane-1, 1-diphosphonic acid, 2-phosphonobutane-1,2,4- tricarboxylic acid, sodium tolytriazole, etc.
Fifthly, since the tracer must be added with the treating agent, the material selected as the tracer must be compatible with the actives (treating agents) such as those enumerated above with respect to formulation, storage, freeze-thaw recovery, etc.
Lastly, the tracer cannot be toxic, or represent any sort of environ metal problem upon discharge. Ideally, any material used in the tracer role would be completely biodegradable.
The enormity of the chemistry complex of on-site water employed in a cooling tower can be appreciated from a mathematical composite of over 500 typical on-site samples subjected to laboratory analysis under our auspices Table I presents the average:
TABLE I ______________________________________ Parameter Concentration ______________________________________ Ca 650 ppm Mg 200 ppm NaCl 200 ppm SO.sub.4 30 ppm pH 8.5 ppm HCO.sub.3 300 ppm CO.sub.3 20 ppm Fe 1.0 ppm Mn 0.1 ppm Cl.sub.2 0.25 ppm NH.sub.3 3 ppm Zn 1.0 ppm SS* 20 mg/l PO.sub.4 10 ppm Na 150 ppm Molybdate 10 ppm K 2 ppm ______________________________________ *suspended solids